Frequency modulated continuous wave radio altimeter spectral monitoring

ABSTRACT

In one embodiment, a radio altimeter tracking filter is provided. The filter comprises: a wireless radio interface; a processor coupled to the wireless radio interface; a memory coupled to the wireless radio interface; wherein the wireless radio interface is configured to wirelessly receive a radio altimeter signal and convert the radio altimeter signal to a baseband frequency signal, wherein the a radio altimeter signal sweeps across a first frequency spectrum between a first frequency and a second frequency; wherein the processor is configured to pass the baseband frequency signal through a filter executed by the processor, the filter comprising a passband having a first bandwidth, and wherein the filter outputs a plurality of spectral chirps in response to the baseband frequency signal passing through the first bandwidth; wherein the processor is configured to process the plurality of spectral chirps to output characteristic parameters that characterize the radio altimeter signal.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to: U.S. patent application Ser. No. ______(attorney docket number H0048645-5883) entitled “COGNITIVE ALLOCATION OFTDMA RESOURCES IN THE PRESENCE OF A RADIO ALTIMETER” filed on even dateherewith and U.S. patent application Ser. No. ______ (attorney docketnumber H0048365-5883) entitled “SYSTEMS AND METHODS TO SYNCHRONIZEWIRELESS DEVICES IN THE PRESENCE OF A FMCW RADIO ALTIMETER” filed oneven date herewith, both of which are incorporated herein by referencein their entirety.

BACKGROUND

Conventional aircraft communication systems including operationalcommunications systems onboard the aircraft, sensors for engines,landing gear and proximity to nearby objects such as vehicles and otheraircraft require complex electrical wiring and harness fabrication,which adds weight to the aircraft and in turn increases fuel costs.Further, these systems are unreliable and difficult to reconfigure, andrely on double or triple redundancy to mitigate the risk of cut ordefective wiring.

The risk of cut or defective wiring can be reduced with the use ofwireless connectivity for wireless avionics devices. However, in manycases the spectrum to be used by the wireless avionics system is alreadyin use by a Radio Altimeter (RA) system as the frequency modulatedcontinuous wave (FMCW) radio altimeter signal sweeps the spectrum.

For the reasons stated above and for other reasons stated below, it willbecome apparent to those skilled in the art upon reading andunderstanding the specification, there is a need in the art formonitoring the signal and determining the parameters necessary to detectthe available spectrum for establishing wireless connectivity in thewireless avionics system.

SUMMARY

The Embodiments of the present disclosure provide systems and methodsfor using a radio altimeter tracking filter to monitor radio altimeterspectrum in an avionics system by reconstruction of the wave created byradio altimeter (RA) frequency modulated continuous wave (FMCW) signal.

In one embodiment, a radio altimeter tracking filter comprises: awireless radio interface; a processor coupled to the wireless radiointerface; a memory coupled to the wireless radio interface; wherein thewireless radio interface is configured to wirelessly receive a radioaltimeter signal and convert the radio altimeter signal to a basebandfrequency signal, wherein the a radio altimeter signal sweeps across afirst frequency spectrum between a first frequency and a secondfrequency; wherein the processor is configured to pass the basebandfrequency signal through a filter executed by the processor, the filtercomprising a passband having a first bandwidth, and wherein the filteroutputs a plurality of spectral chirps in response to the basebandfrequency signal passing through the first bandwidth; wherein theprocessor is configured to process the plurality of spectral chirps tooutput characteristic parameters that characterize the radio altimetersignal.

DRAWINGS

Understanding that the drawings depict only exemplary embodiments andare not therefore to be considered limiting in scope, the exemplaryembodiments will be described with additional specificity and detailthrough the use of the accompanying drawings, in which:

FIG. 1 is a high level block diagram of one embodiment of an exemplaryavionics system 100;

FIG. 1A is a block diagram of an example radio altimeter tracking filterincluded in one embodiment of the present disclosure;

FIGS. 2A and 2B is a graphical representation of spectral chirps causedby the RA FMCW signal of one embodiment of the present disclosure;

FIG. 3A is a magnified view of an example of spectral chirps of a downconverted RA FMCW signal of one embodiment of the present disclosure;

FIG. 3B is a graphical representation of ambiguity in slopedetermination of a down converted RA FMCW signal of one embodiment ofthe present disclosure.

FIG. 3C is a graphical representation of an example of reconstructedwave created by the RA FMCW signal of one embodiment of the presentdisclosure;

FIG. 4A is a graphical representation of down-converted I-signal andQ-signal in time domain of one embodiment of the present disclosure;

FIG. 4B is a graphical representation of an example of the reconstructedwave within the filter bandwidth of the allocated frequency spectrum ofone embodiment of the present disclosure;

FIG. 5 is a flow chart illustrating a method of one embodiment of thepresent disclosure.

In accordance with common practice, the various described features arenot drawn to scale but are drawn to emphasize specific features relevantto the exemplary embodiments.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings that form a part hereof, and in which is shown byway of illustration specific illustrative embodiments. These embodimentsare described in sufficient detail to enable those skilled in the art topractice the invention, and it is to be understood that otherembodiments may be utilized and that logical, mechanical, and electricalchanges may be made. The following detailed description is, therefore,not to be taken in a limiting sense.

Embodiments of the present disclosure provide systems and methods formonitoring radio altimeter spectrum in an avionics system byreconstruction of the wave created by radio altimeter (RA) frequencymodulated continuous wave (FMCW) signal. This wave can be reconstructedby determining the slope and the period of the FMCW from the chirpscaused by the RA FMCW signal sweeping through filter bandwidth. Further,the embodiments of the present disclosure resolve the ambiguity in themagnitude of the slope of such an FMCW signal.

Once the parameters of this wave are determined, these parameters can beused by various communication systems to communicate over the bandwidthallocated to the radio altimeter. In one example, these parameters canbe used by a wireless avionics system utilizing a time division multipleaccess (TDMA) scheme. In such a system, the wireless avionics systemuses the parameters to reconstruct the FMCW signal and allocate timeslots and frequency of the TDMA signal to avoid interference with the RAsignal.

FIG. 1 is a block diagram illustrating a wireless device network 100 ofone embodiment of the present disclosure. In some implementations,wireless device network 100 may comprise a wireless avionics network. Itshould be understood that the systems and methods of the presentdisclosure are applicable to any network using a wireless communicationsprotocol that needs to avoid a signal that periodically sweeps abandwidth.

System 100 includes a plurality of device nodes 102 (also referred toherein as wireless avionics device nodes 110), one or more of whichcomprise wireless avionics sensors. Wireless avionics devices 110 sharea radio frequency spectrum using TDMA where each device 102 is grantedaccess to transmit over an RF channel during a specified timeslotallocated to them by a Wireless Avionics Timeslot Allocation Function136. In one embodiment, each frame comprises 2000 timeslots and each2000 timeslot frame has a duration of one second.

Wireless device network 100 further comprises a Wireless AvionicsTimeslot Allocation Function 136 that is aware of the sweeping radioaltimeter signal 132 produced by the on-board radio altimeter 130 andallocates time slots to wireless avionics device nodes that will avoidtransmitting on frequencies currently occupied by radio altimeter signal132. Wireless Avionics Timeslot Allocation Function 136 is coupled to aRadio Altimeter Tracking Filter 134 that receives the radio altimetersignal 132 and characterizes the signal 132 into descriptive parameters(discussed below) used by Wireless Avionics Timeslot Allocation Function136 to predictively determine which wireless avionics channels areavailable during which timeslots, and which wireless avionics channelsare to be avoided during which timeslots. In one embodiment, RadioAltimeter Tracking Filter 134 characterizes the radio altimeter signal132 transmitted by the aircraft's radio altimeter 130 and characterizesthe signal 132 by determining parameters such as the current amplitudeand period of the radio altimeter signal pattern, for example. Inexemplary embodiments, the signal 132 is a triangle wave, a square wave,or another suitable wave for a radio altimeter known to one having skillin the art.

Allocation of timeslots to wireless avionics devices 110 is the subjectof U.S. patent application Ser. No. ______ which is incorporated hereinby reference. In short, Wireless Avionics Timeslot Allocation Function136 is provided by Radio Altimeter Tracking Filter 134 inputs includingthe current amplitude and period of the radio altimeter 130 signalpattern as well as the current frequency and/or channels occupied by theradio altimeter signal 132. Using this data from Radio AltimeterTracking Filter 134, Wireless Avionics Timeslot Allocation Function 136allocates timeslots to each of the wireless avionics devices 110 whichare calculated not to conflict with the radio altimeter signal 132.

In this example, the radio altimeter 130 is allocated a spectrum of 4200MHz-4400 MHz. However, the radio altimeter 106 may only utilize aportion of the allocated spectrum. For example, the radio altimeter 130may only utilize a span of 4235 MHz-4365 MHz. It is to be understoodthat other frequency spectra can be allocated for use by the radioaltimeter 106 in other embodiments. Similarly, the radio altimeter 130may utilize other portions of the allocated spectrum in otherembodiments. The radio altimeter signal 132 interacts with the ground orsurface beneath the aircraft and part of the incident signal tonereflects back to the radio altimeter 130. By measuring the amount oftime it takes to receive the reflection, the radio altimeter 130 is ableto determine the altitude of the aircraft on which the wireless avionicssystem 100 is located. Operation of a radio altimeter 130 is known toone of skill in the art and not discussed in more detail herein.

The radio altimeter signal 132 is swept through the frequency spectrumallocated for the operation of the wireless avionics system 100. Becausethe signal 132 is sweeping, the radio altimeter 130 is only using aportion of the allocated spectrum shared with wireless avionics system100 at a given point in time. The Radio Altimeter Tracking Filter 134 isconfigured to track characteristics of the radio altimeter signal 132.In particular, the Radio Altimeter Tracking Filter 134 tracks theperiodicity, sweep rate, and the amplitude of the signal tone of theradio altimeter during the present frame of communication. The RadioAltimeter Tracking Filter 134 is also configured to predict these valuesinto the future. In exemplary embodiments, the Radio Altimeter TrackingFilter 134 predicts the frequency of the radio altimeter signal into thefuture using the following equation:

$\begin{matrix}{{Frequency} = {( \frac{d}{p} )*( {P - {{abs}( {{t\mspace{14mu} \% ( {2*P} )} - P} )}} )}} & (1)\end{matrix}$

where: A is the amplitude, P is the period of the sweep, and t is time.In particular, the Radio Altimeter Tracking Filter 134 predicts thefrequency of the signal 132 of the radio altimeter for the next frame ofcommunication during the present frame of communication. For example, inone embodiment, during frame 1, the Radio Altimeter Tracking Filter 134predicts the frequency of the radio altimeter signal 132 for all pointsin time in frame 2. In other exemplary embodiments, the Radio AltimeterTracking Filter 134 predicts the frequency of the signal further intothe future. The amount of time into the future that the module canpredict is limited by the accuracy of the prediction. Since the radioaltimeter and the wireless device system may both be critical to flightsafety, interference cannot occur between the radio altimeter signal 132and the TDMA signals transmitted by the wireless avionics device nodes102.

The Radio Altimeter Tracking Filter 134 provides the predicted frequencyof the radio altimeter signal tone to the Timeslot Allocation Function136. Based on the predicted frequency of the radio altimeter signaltone, the Timeslot Allocation Function 136 is configured to allocatetime slots on a TDMA basis to the wireless avionics device nodes 102 inthe unused portion of the frequency spectrum not currently in use by theradio altimeter 106 and to prevent transmission over particular channelsat time slots when they correspond to the frequency of the radioaltimeter signal tone 132. In other words, the Timeslot AllocationFunction 136 is configured to allocate time slots and frequencies of theTDMA signals so the TDMA signals do not overlap with the frequency ofthe signal 132 from the radio altimeter 130.

FIG. 1A is a diagram illustrating one implementation of Radio AltimeterTracking Filter 134 comprises a wireless radio interface 186 coupled toa processor 182 and memory 184. Memory 184 may be an internal memory andcomprised within processor 182. In some examples, memory 184 may be anexternal memory coupled to processor 182. In this implementation, RadioAltimeter Tracking Filter 134 utilizes a direct conversion to basebandapproach to detect the radio altimeter signal 132. Accordingly, in oneembodiment, wireless radio interface 186 comprises a receiver, ortransceiver that is able to operate over the spectrum swept by radioaltimeter signal 132. For example, in one implementation, wireless radiointerface 186 comprises an RF Agile Transceiver capable of operating inthe Aeronautical Radio Navigation Band (4.2.-4.4 GHz) with which radioaltimeter signal 132 is digitally sampled (using analog to digitalconverter 190, for example) and down converted to a baseband frequency(using digital down converter 192, for example). The result is processedby processor 182 to detect the spectral chirps in the sweeping radioaltimeter signal 132.

In one embodiment, wireless radio interface 186 receives signal 132 andis configured to sample, filter and process the down converted in-phase(I-signal) and quadrature (Q-signal) to detect the spectral chirps.Alternatively, in some embodiments, A/D converter 190 is configured tosample the received signal 132 and convert the signal from analog todigital, digital down converter 192 filters the sampled signal to outputbaseband in-phase (I) and quadrature phase (Q) component signals, and aprocessor 182 that processes the I and the Q signal components to detectthe spectral chirps caused by signal 132 sweeping through the allocatedfrequency spectrum. The slope, period or other characteristic parametersof the radio altimeter signal 132 can be computed from the spectralchirps detected at baseband. In one embodiment, these parameters arethen communicated to one or more avionics components coupled to theRadio Altimeter Tracking Filter 134 (such as, but not limited to, theWireless Avionics Timeslot Allocation Function 134, for example). In oneembodiment, the characteristic parameters are stored in a memory 184 andcan be accessed by one or more avionics component at a later time.

Network 100 further includes a filter that has a passband falling(filter bandwidth) within the frequency spectrum swept by the RA. Asshown in FIG. 1A, in one example, this filter is implemented as anfinite impulse response (FIR) filter 188 executed by processor 182. Inone example, bandwidth of passband of filter 188 is 100 MHz. In afurther example, the bandwidth of the passband of filter 188 is in arange of 4.25 GHz and 4.35 GHz. FIGS. 2A and 2B depict an example ofspectral chirps caused by the RA FMCW signal sweeping through allocatedfrequency spectrum as detected at baseband. FIG. 2A depicts the I-signaldetected at baseband and FIG. 2B depicts the Q-signal detected atbaseband. Each time the signal passes through the passband of filter188, it produces an output from the filter in the form of a chirp thathas a specific slope and duration. After the I-signal and the Q-signalis processed, the RA FMCW is characterized by determination of the RFsignal's slope, slope magnitude, and period.

FIG. 3A is a magnified view of an example of spectral chirps from timet1 to t8 caused by the radio altimeter signal 132 sweeping through thebandwidth of filter 188. As seen in the example in FIG. 3A, a firstchirp c1 is caused from time t1 to t2, a second chirp c2 is caused fromtime t3 to t4, a third chirp c3 is caused from time t5 to t6 and afourth chirp c4 is caused from time t7 to t8. Chirps c1, c2, c3 and c4are caused when the radio altimeter signal 132 is within the passband offilter 188.

The absolute slope of a chirp, such as chirp c1 for example, can bedetermined by the following equation 2:

Absolute Slope=Bandwidth/(t2−t1)  (2)

where: t2−t1 is a difference between the point in time when the chirpbegins (t1) and the point in time when the chirp ends (t2) andBandwidth, is the bandwidth of the passband of filter 188. Thecalculated result ml is the magnitude of the absolute slope of thereconstructed wave. The absolute slope of the reconstructed wave atother chirps c2, c3 and c4 is similarly calculated.

However, since a chirp is created every time the signal passes throughthe bandwidth of passband of filter 188 within the allocated frequencyspectrum, the chirp could be created either when the signal 132 passesthrough the passband of the filter 188 as its frequency increases andthe slope is positive, or when the signal passes through the passband offilter 188 as its frequency decreases and the slope is negative. Thisambiguity in slope is shown by FIG. 3B. As shown in FIG. 3B, because ofthe slope ambiguity either a first wave 301 or a second wave 302,reverse of the wave 301 could be reconstructed using the absolute slopecalculated in equation (2).

This slope ambiguity can be resolved by monitoring the frequency ofsignal 132 as it sweeps past passband midpoint 410 a, the midpoint ofthe passband of filter 188. In one example, signal 132 sweeps past alocal oscillator comprised within filter 188 and passband midpoint 410 ais a zero point. FIG. 4A is a graphical representation of an example ofthe down-converted I-signal and the Q-signal as the frequency sweepsthrough filter 188. As shown in FIG. 4A, the sinusoid of I-signal 401 isleading the sinusoid of Q-signal 402 until the signals cross passbandmidpoint 410 a. After passband midpoint 410 a, sinusoid of Q-signal 402is leading sinusoid of I-signal 401. Thus, the slope ambiguity can beresolved by monitoring the frequency of the detector as crosses thepassband midpoint.

FIG. 4B is a graphical representation of an example of the reconstructedwave within the passband of the allocated frequency spectrum. Thebandwidth of the passband in FIG. 4B is 100 MHz. In the example shown inFIG. 4B, the frequency wave is reconstructed using the signals shown inFIG. 4A. Accordingly, the passband midpoint 410 a of FIG. 4A is the sameas passband midpoint 410 b shown in FIG. 4B. As shown in FIG. 4B, theslope of the reconstructed wave 403 is determined positive when thefrequency switches from sinusoid of I-signal 401 leading to sinusoid ofQ-signal leading after it crosses the passband midpoint 410 b. Likewise,the slope of the reconstructed wave is determined negative when thefrequency switches from sinusoid of Q-signal leading to I-signal leadingafter it crosses the passband midpoint 410 b.

The period of the radio altimeter signal is the duration of time of onecycle of the signal after which the cycle of the signal will berepeated. As discussed above, a chirp could be created either when thesignal passes through the passband as its frequency increases and theslope is positive, or when the signal passes through the passband as itsfrequency decreases and the slope is negative. Thus, the signal willchirp twice in one period: once, as the signal passes through thepassband while its frequency is increasing and once, as the signalpasses through the passband while its frequency is decreasing.Therefore, the period of the signal can be determined from the time thefirst chirp begins until the time the third chirp begins.

Referring back to the example of FIG. 3A, chirps c1, c2, c3 and c4 aregenerated by the radio altimeter signal 132 as the signal passes throughthe passband of filter 188 while sweeping through the allocatedfrequency spectrum. Chirps c1 and c3 have a positive slope and chirps c2and c4 have a negative slope. Thus, one cycle of signal 132 extends fromtime t1, when the first chirp begins to time t5, when the third chirpbegins and the cycle repeats. The period of the signal can be determinedby the following equation 3:

Period=(t5−t1)=(t6−t2)=(t7−t3)=(t8−t4)  (3)

where: t5−t1 is the difference between the point in time t5 when chirpc3 begins and the point in time t1 when chirp c1 begins. Similarly, theperiod can be determined by calculating the difference between the timet6 when chirp c3 ends and time t2 when chirp c1 ends, or the differencebetween time t7 when chirp c4 begins and time t3 when chirp c2 begins,or the difference between time t8 when chirp c4 ends and time t4 whenchirp c2 ends.

FIG. 3C is a graphical representation of an example of reconstructedwave 303 created by the RA's FMCW signal as the signal sweeps through anallocated frequency spectrum within a passband 315 having a bandwidthwithin the allocated frequency spectrum. The allocated frequencyspectrum in the example shown in FIG. 3C ranges from 4.2 GHz to 4.4 GHz.As shown in FIG. 3C, wave sections 304 are parts of the wave 303 withinbandwidth 315. In one implementation, the example wave shown in FIG. 3Cis reconstructed from the chirps shown in FIG. 3A.

As seen in FIGS. 3A-3C, wave sections 304 are reconstructed from thecharacteristics of their respective corresponding chirps. For example,in FIG. 3A, the frequency of the RF signal switches from sinusoid ofI-signal leading to sinusoid of Q-signal leading after it crosses thepassband midpoint 310-1. Accordingly, wave section 304-1 has a positiveslope with a magnitude of ml (calculated using equation (2)). Likewise,wave sections 304-2, 304-3, and 304-4 have the characteristics of chirpsc2, c3 and c4 respectively.

FIG. 5 is a flow diagram of an example method 500 of monitoring afrequency modulated continuous wave radio altimeter spectrum.

Method 500 begins at block 502 with receiving a radio altimeter (RA)radio frequency (RF) signal. Method 500 proceeds to block 504 withdown-converting the received radio altimeter (RA) signal, wherein the RARF signal sweeps across a first frequency spectrum between a firstfrequency and a second frequency. In some implementations, the receivedradio altimeter is converted to a baseband signal. In one example,converting a RA RF signal to a baseband signal further comprises directdown converting the RA RF signal. In one example, the RA RF signal isdown converted using a RF agile transceiver. In some examples, the RFagile transceiver can operate in a band ranging from 4.2 GHz to 4.4 GHzinclusive.

Method 500 proceeds to block 506 with filtering the down-convertedsignal by passing the down-converted signal through a filter with apassband having a first bandwidth to output a plurality of spectralchirps in response to passing the down-converted signal through thefirst bandwidth. In one example, filtering the down-converted signalfurther comprises passing the down-converted signal through a passbandhaving a first bandwidth of 100 MHz. In a further example, the firstbandwidth ranges from 4.25 GHz to 4.35 GHz.

Method 500 proceeds to block 508 with processing the plurality ofspectral chirps to output characteristic parameters that characterizethe RA RF signal. In one example, processing the plurality of spectralchirps further comprises calculating a first characteristic parametercomprising a period of the RA RF signal, calculating a secondcharacteristic parameter comprising an absolute slope of the RA RFsignal, and calculating a third characteristic parameter comprising amagnitude of the absolute slope, wherein the magnitude of the absoluteslope is determined based on a relative phase difference between thein-phase component and the quadrature-phase component of thedown-converted signal.

In one example of method 500, calculating the first characteristicparameter further comprises determining the absolute slope as a functionof division of a first difference between a first point in time and asecond point time by the filter bandwidth, wherein the first point intime is time when a respective chirp begins and the second point in timeis time when the respective chirp ends. In an example of method 500,calculating the second characteristic further comprises determining theperiod is a second difference between a first point in time and a thirdpoint in time, wherein the first point in time is when a first chirpbegins and the third point in time is when a second chirp begins,wherein the first chirp and the second chirp have the same slope. In oneexample, calculating a third characteristic further comprisesdetermining magnitude of the absolute slope as positive when theI-signal's sinusoid is leading the Q-signal's sinusoid before a passbandmidpoint and the Q-signal's sinusoid is leading an I-signal's sinusoidafter the passband midpoint, and determining the slope as negative whenthe Q-signal's sinusoid is leading the I-signal's sinusoid before apassband midpoint and the I-signal's sinusoid is leading the Q-signal'ssinusoid after the passband midpoint. In one example, method 500 furthercomprises communicating the characteristic parameters to one or moreavionics components.

Example Embodiments

Example 1 includes a radio altimeter tracking filter, the filtercomprising: a wireless radio interface; a processor coupled to a memory;wherein the wireless radio interface is configured to wirelessly receivea radio altimeter signal and convert the radio altimeter signal to abaseband frequency signal, wherein the a radio altimeter signal sweepsacross a first frequency spectrum between a first frequency and a secondfrequency; wherein the processor is configured to pass the basebandfrequency signal through a filter executed by the processor, the filtercomprising a passband having a first bandwidth, and wherein the filteroutputs a plurality of spectral chirps in response to the basebandfrequency signal passing through the first bandwidth; wherein theprocessor is configured to process the plurality of spectral chirps tooutput characteristic parameters that characterize the radio altimetersignal.

Example 2 includes the filter of Example 1, wherein the basebandfrequency signal comprises in-phase (I) component and a quadrature-phase(Q) component; wherein the processor calculates: a first characteristicparameter comprising a period of the radio altimeter signal; a secondcharacteristic parameter comprising an absolute slope of the radioaltimeter signal; and a third characteristic parameter comprising amagnitude of the absolute slope, wherein the magnitude of the absoluteslope is determined based on a relative phase difference between thein-phase component and the quadrature-phase component of the basebandfrequency signal.

Example 3 includes the filter of Example 2, wherein the slope is definedas positive when the I-phase component leads Q-phase component beforethe baseband frequency signal crosses a passband midpoint and theQ-phase component is leading the I-phase component after the passbandmidpoint, and wherein the slope is defined as negative when Q-phasecomponent is leading the I-phase component before a passband midpointand the -phase component is leading the Q-phase component after thepassband midpoint.

Example 4 includes the filter of any of Examples 2-3, wherein theabsolute slope is a result of division of a first difference between afirst point in time and a second point time by the first bandwidth,wherein the first point in time is time when a respective chirp beginsand the second point in time is time when the respective chirp ends.

Example 5 includes the filter of any of Examples 2-4, wherein the periodis a second difference between a first point in time and a third pointin time, wherein the first point in time is when a first chirp beginsand the third point in time is when a second chirp begins, wherein thefirst chirp and the second chirp have the same slope.

Example 6 includes the filter of any of Examples 1-5, wherein thewireless radio interface further comprises a receiver or transceiverable to operate over the first frequency spectrum.

Example 7 includes the filter of any of Examples 1-6, wherein thewireless radio interface comprises an RF Agile Transceiver capable ofoperating in the first frequency spectrum.

Example 8 includes the filter of any of Examples 1-7, wherein the firstfrequency spectrum is Aeronautical Radio Navigation Band ranging fromExample 4.2 GHz to any of Examples 4-7.4 GHz.

Example 9 includes the filter of any of Examples 1-8, wherein thewireless radio interface further comprises an analog-to-digitalconverter and a digital down converter.

Example 10 includes the filter of any of Examples 1-9, wherein the firstbandwidth is 100 MHz and ranges from Example 4.25 GHz to any of Examples4-9.35 GHz.

Example 11 includes the filter Example 1, wherein the processor isfurther configured to communicate characteristic parameters to one ormore avionics components coupled to the filter.

Example 12 includes the avionics system of any of Examples 1-11, whereinthe baseband frequency signal is a triangle wave.

Example 13 includes a method of monitoring radio altimeter spectrum inan avionics system, the method comprising: receiving a radio altimeter(RA) radio frequency (RF) signal; converting the RA RF signal, whereinthe RA RF signal sweeps across a first frequency spectrum between afirst frequency and a second frequency; filtering the down-convertedsignal by passing the down-converted signal through a passband having afirst bandwidth to output a plurality of spectral chirps in response topassing the down-converted signal through the first bandwidth; andprocessing the plurality of spectral chirps to output characteristicparameters that characterize the RA RF signal.

Example 14 includes the method of Example 14, wherein converting the RARF signal further comprises converting the RA RF signal to a basebandfrequency signal.

Example 15 includes the method of any of Examples 13-14, whereinprocessing the plurality of spectral chirps further comprises:calculating a first characteristic parameter comprising a period of theRA RF signal; calculating a second characteristic parameter comprisingan absolute slope of the RA RF signal; and calculating a thirdcharacteristic parameter comprising a magnitude of the absolute slope,wherein the magnitude of the absolute slope is determined based on arelative phase difference between an in-phase (I) component and a (Q)quadrature-phase component of the down-converted signal.

Example 16 includes the method of Example 15, wherein calculating athird characteristic further comprises determining magnitude of theabsolute slope as positive when the I-signal's sinusoid is leading theQ-signal's sinusoid before a passband midpoint and the Q-signal'ssinusoid is leading an I-signal's sinusoid after the passband midpoint,and determining the slope as negative when the Q-signal's sinusoid isleading the I-signal's sinusoid before a passband midpoint and theI-signal's sinusoid is leading the Q-signal's sinusoid after thepassband midpoint.

Example 17 includes the method of any of Examples 15-16, whereincalculating the first characteristic parameter further comprisesdetermining the absolute slope is a result of division of a firstdifference between a first point in time and a second point time by thefilter bandwidth, wherein the first point in time is time when arespective chirp begins and the second point in time is time when therespective chirp ends.

Example 18 includes the method of any of Examples 15-17, whereincalculating the second characteristic further comprises determining theperiod is a second difference between a first point in time and a thirdpoint in time, wherein the first point in time is when a first chirpbegins and the third point in time is when a second chirp begins,wherein the first chirp and the second chirp have the same slope.

Example 19 includes a wireless communication system, the systemcomprising: a plurality of device nodes aboard an aircraft that share aradio frequency spectrum using time-division multiple access (TDMA); aradio altimeter tracking filter configured to output characteristicparameters characterizing a radio altimeter signal transmitted by aradio altimeter aboard the aircraft; a timeslot allocation functioncoupled to the radio altimeter tracking filter, wherein the timeslotallocation function allocates timeslots to channels within the radiofrequency spectrum based on the characterization parameters; wherein theradio altimeter tracking filter is configured to wirelessly receive theradio altimeter signal and convert the radio altimeter signal to abaseband frequency signal, wherein the a radio altimeter signal sweepsacross the radio frequency spectrum between a first frequency and asecond frequency; wherein the radio altimeter tracking filter implementsa filter comprising a passband having a first filter bandwidth, whereinthe filter outputs a plurality of spectral chirps in response to thebaseband frequency signal passing through the first bandwidth; whereinthe radio altimeter tracking filter is configured to process theplurality of spectral chirps to output the characteristic parametersthat characterize the radio altimeter signal.

Example 20 includes the system of Example 19, wherein there basebandfrequency signal comprises in-phase (I) component and a quadrature-phase(Q) component; wherein the characteristic parameters comprise at least:a first characteristic parameter comprising a period of the radioaltimeter signal; a second characteristic parameter comprising anabsolute slope of the radio altimeter signal; and a third characteristicparameter comprising a magnitude of the absolute slope, wherein themagnitude of the absolute slope is determined based on a relative phasedifference between the in-phase component and the quadrature-phasecomponent of the baseband frequency signal.

In various alternative embodiments, system elements, method steps, orexamples described throughout this disclosure (such as the wirelessavionics devices, Wireless Avionics Timeslot Allocation Function, RadioAltimeter Tracking Filter, or sub-parts thereof, for example) may beimplemented using one or more computer systems, field programmable gatearrays (FPGAs), or similar devices comprising a processor coupled to amemory (such as shown in FIG. 1, for example) and executing code torealize those elements, processes, or examples, said code stored on anon-transient data storage device. Therefore other embodiments of thepresent disclosure may include elements comprising program instructionsresident on computer readable media which when implemented by suchcomputer systems, enable them to implement the embodiments describedherein. As used herein, the term “computer readable media” refers totangible memory storage devices having non-transient physical forms.Such non-transient physical forms may include computer memory devices,such as but not limited to punch cards, magnetic disk or tape, anyoptical data storage system, flash read only memory (ROM), non-volatileROM, programmable ROM (PROM), erasable-programmable ROM (E-PROM), randomaccess memory (RAM), or any other form of permanent, semi-permanent, ortemporary memory storage system or device having a physical, tangibleform. Program instructions include, but are not limited tocomputer-executable instructions executed by computer system processorsand hardware description languages such as Very High Speed IntegratedCircuit (VHSIC) Hardware Description Language (VHDL).

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement, which is calculated to achieve the same purpose,may be substituted for the specific embodiments shown. Therefore, it ismanifestly intended that this invention be limited only by the claimsand the equivalents thereof.

What is claimed is:
 1. A radio altimeter tracking filter, the filtercomprising: a wireless radio interface; a processor coupled to thewireless radio interface; a memory coupled to the wireless radiointerface; wherein the wireless radio interface is configured towirelessly receive a radio altimeter signal and convert the radioaltimeter signal to a baseband frequency signal, wherein the a radioaltimeter signal sweeps across a first frequency spectrum between afirst frequency and a second frequency; wherein the processor isconfigured to pass the baseband frequency signal through a filterexecuted by the processor, the filter comprising a passband having afirst bandwidth, and wherein the filter outputs a plurality of spectralchirps in response to the baseband frequency signal passing through thefirst bandwidth; wherein the processor is configured to process theplurality of spectral chirps to output characteristic parameters thatcharacterize the radio altimeter signal.
 2. The filter of claim 1,wherein the baseband frequency signal comprises in-phase (I) componentand a quadrature-phase (Q) component; wherein the processor calculates:a first characteristic parameter comprising a period of the radioaltimeter signal; a second characteristic parameter comprising anabsolute slope of the radio altimeter signal; and a third characteristicparameter comprising a magnitude of the absolute slope, wherein themagnitude of the absolute slope is determined based on a relative phasedifference between the in-phase component and the quadrature-phasecomponent of the baseband frequency signal.
 3. The filter of claim 2,wherein the slope is defined as positive when the I-phase componentleads Q-phase component before the baseband frequency signal crosses apassband midpoint and the Q-phase component is leading the I-phasecomponent after the passband midpoint, and wherein the slope is definedas negative when Q-phase component is leading the I-phase componentbefore a passband midpoint and the -phase component is leading theQ-phase component after the passband midpoint.
 4. The filter of claim 2,wherein the absolute slope is a result of division of a first differencebetween a first point in time and a second point time by the firstbandwidth, wherein the first point in time is time when a respectivechirp begins and the second point in time is time when the respectivechirp ends.
 5. The filter of claim 2, wherein the period is a seconddifference between a first point in time and a third point in time,wherein the first point in time is when a first chirp begins and thethird point in time is when a second chirp begins, wherein the firstchirp and the second chirp have the same slope.
 6. The filter of claim1, wherein the wireless radio interface further comprises a receiver ortransceiver able to operate over the first frequency spectrum.
 7. Thefilter of claim 1, wherein the wireless radio interface comprises an RFAgile Transceiver capable of operating in the first frequency spectrum.8. The filter of claim 1, wherein the first frequency spectrum isAeronautical Radio Navigation Band ranging from 4.2 GHz to 4.4 GHz. 9.The filter of claim 1, wherein the wireless radio interface furthercomprises an analog-to-digital converter and a digital down converter.10. The filter of claim 1, wherein the first bandwidth is 100 MHz andranges from 4.25 GHz to 4.35 GHz.
 11. The filter claim 1, wherein theprocessor is further configured to communicate characteristic parametersto one or more avionics components coupled to the filter.
 12. Theavionics system of claim 1, wherein the baseband frequency signal is atriangle wave.
 13. A method of monitoring radio altimeter spectrum in anavionics system, the method comprising: receiving a radio altimeter (RA)radio frequency (RF) signal; converting the RA RF signal, wherein the RARF signal sweeps across a first frequency spectrum between a firstfrequency and a second frequency; filtering the down-converted signal bypassing the down-converted signal through a passband having a firstbandwidth to output a plurality of spectral chirps in response topassing the down-converted signal through the first bandwidth; andprocessing the plurality of spectral chirps to output characteristicparameters that characterize the RA RF signal.
 14. The method of claim14, wherein converting the RA RF signal further comprises converting theRA RF signal to a baseband frequency signal.
 15. The method of claim 13,wherein processing the plurality of spectral chirps further comprises:calculating a first characteristic parameter comprising a period of theRA RF signal; calculating a second characteristic parameter comprisingan absolute slope of the RA RF signal; and calculating a thirdcharacteristic parameter comprising a magnitude of the absolute slope,wherein the magnitude of the absolute slope is determined based on arelative phase difference between an in-phase (I) component and a (Q)quadrature-phase component of the down-converted signal.
 16. The methodof claim 15, wherein calculating a third characteristic furthercomprises determining magnitude of the absolute slope as positive whenthe I-signal's sinusoid is leading the Q-signal's sinusoid before apassband midpoint and the Q-signal's sinusoid is leading an I-signal'ssinusoid after the passband midpoint, and determining the slope asnegative when the Q-signal's sinusoid is leading the I-signal's sinusoidbefore a passband midpoint and the I-signal's sinusoid is leading theQ-signal's sinusoid after the passband midpoint.
 17. The method of claim15, wherein calculating the first characteristic parameter furthercomprises determining the absolute slope is a result of division of afirst difference between a first point in time and a second point timeby the filter bandwidth, wherein the first point in time is time when arespective chirp begins and the second point in time is time when therespective chirp ends.
 18. The method of claim 15, wherein calculatingthe second characteristic further comprises determining the period is asecond difference between a first point in time and a third point intime, wherein the first point in time is when a first chirp begins andthe third point in time is when a second chirp begins, wherein the firstchirp and the second chirp have the same slope.
 19. A wirelesscommunication system, the system comprising: a plurality of device nodesaboard an aircraft that share a radio frequency spectrum usingtime-division multiple access (TDMA); a radio altimeter tracking filterconfigured to output characteristic parameters characterizing a radioaltimeter signal transmitted by a radio altimeter aboard the aircraft; atimeslot allocation function coupled to the radio altimeter trackingfilter, wherein the timeslot allocation function allocates timeslots tochannels within the radio frequency spectrum based on thecharacterization parameters; wherein the radio altimeter tracking filteris configured to wirelessly receive the radio altimeter signal andconvert the radio altimeter signal to a baseband frequency signal,wherein the a radio altimeter signal sweeps across the radio frequencyspectrum between a first frequency and a second frequency; wherein theradio altimeter tracking filter implements a filter comprising apassband having a first filter bandwidth, wherein the filter outputs aplurality of spectral chirps in response to the baseband frequencysignal passing through the first bandwidth; wherein the radio altimetertracking filter is configured to process the plurality of spectralchirps to output the characteristic parameters that characterize theradio altimeter signal.
 20. The system of claim 19, wherein therebaseband frequency signal comprises in-phase (I) component and aquadrature-phase (Q) component; wherein the characteristic parameterscomprise at least: a first characteristic parameter comprising a periodof the radio altimeter signal; a second characteristic parametercomprising an absolute slope of the radio altimeter signal; and a thirdcharacteristic parameter comprising a magnitude of the absolute slope,wherein the magnitude of the absolute slope is determined based on arelative phase difference between the in-phase component and thequadrature-phase component of the baseband frequency signal.